During conventional drilling procedures, it is often desirable to conduct various tests of the wellbore and drill string while the drill string is still in the wellbore. These tests are commonly referred to as drill stem tests (“DST”). To facilitate DST, a subsea test tree (“SSTT”) carried by the drill string is positioned within the BOP stack. The SSTT is provided with one or more valves that permit the wellbore to be isolated as desired, for the performance of DST. The SSTT also permits the drill string below the SSTT to be disconnected at the seabed, without interfering with the function of the BOP. In this regard, the SSTT serves as a contingency in the event of an emergency that requires disconnection of the drillstring in the wellbore from the surface, such as in the event of severe weather or malfunction of a dynamic positioning system. As such, the SSTT includes a decoupling mechanism to unlatch the portion of the drill string in the wellbore from the drill string above the wellbore. Thereafter, the surface vessel and riser can decouple from the BOP and move to safety. Finally, the SSTT typically is deployed in conjunction with a fluted hanger disposed to land at the top of the wellbore to at least partially support the lower portion of the drillstring during DST.
Before DST, however, proper positioning of the SSTT within the BOP is important so as to prevent the SSTT from interfering with operation of the BOP. In particular, if the SSTT is not correctly spaced apart from the hanger, proper functioning of the BOP rams may be inhibited. Moreover, the SSTT may be destroyed by the rams to the extent the rams are activated for a particular reason. Accordingly, a “dummy run” is conducted before DST to determine positioning of the SSTT within the BOP, and in particular the spacing of the fluted hanger from the SSTT so that the SSTT components are positioned between the BOP rams.
During conventional dummy runs, a temporary hanger with a painted pipe above it is run into the BOP, typically on jointed tubing. Once the temporary hanger lands within the BOP, the rams are closed on the painted pipe with sufficient pressure to leave marks that indicate their position relative to the landed hanger. The rams are then retracted, and the dummy string is retrieved uphole. Based upon the markings on the painted pipe, proper positioning of the SSTT within the BOP is determined and the spacing of the fluted hanger from the SSTT is accordingly adjusted at the surface to achieve the desired positioning when the SSTT is deployed in the BOP.
Although simplistic, there is at least one severe drawback to conventional dummy run operations. Making up the jointed tubing used in the dummy assembly is very time consuming. Given this, and the fact that some wells are drilled at ocean depths of up to 10,000 feet or deeper, it can take days to complete a single dummy run. At the present time, it is estimated that some floating rigs have a daily cost of upwards of 400,000 USD. Therefore, conventional dummy run operations are very expensive.
In view of the foregoing, there is a need in the art for cost-effective approaches to proper positioning of the subsea test equipment within the BOP.